CN1069401C - Method for profiling object surface using large equivalent wavelength and system therefor - Google Patents

Method for profiling object surface using large equivalent wavelength and system therefor Download PDF

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CN1069401C
CN1069401C CN95118298A CN95118298A CN1069401C CN 1069401 C CN1069401 C CN 1069401C CN 95118298 A CN95118298 A CN 95118298A CN 95118298 A CN95118298 A CN 95118298A CN 1069401 C CN1069401 C CN 1069401C
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interference
desensitization
light
illumination
measurement data
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CN1147627A (en
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彼德·德·格鲁特
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Zygo Corp
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    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/30—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces
    • G01B11/306—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces for measuring evenness

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Abstract

A method and system for profiling an object surface at a convenient working distance to the object using desensitized interference images. Data for one or more image points or pixels in the field of view of the interferometer are generated by displacing the object with respect to the interferometer while at the same time recording detecter data in electronic memory. The variation of intensity as a function of scan position may be described as an approximately oscillator signal related to the equivalent wavelength, modulated by a signal envelope that limits the interference effect to a range within the equivalent coherence length. By analysis of the interference pattern with the computer a surface height is determined which corresponds to each of the image pixels.

Description

Utilize the method and system of big effective wavelength Measuring Object surface profile
The present invention relates generally to the precise measurement technique of surface imagery and analysis, especially relate to the optical non-contact measurement method of surface profile.
A common manufacturing issue is the precision measurement of surface topography.The example that many processing projects need be measured is, the parts of the parts of engine, magnetic memory, flat-panel screens, molded and frosting textured, the coin of mechanical pump surface and sealing and casting.Producing efficiently in industrial production environment needs at a high speed automated quality control.
The most frequently used surface profile measurement instrument is mechanical contact pilotage, and work slowly only provides finite information, also may form damage to body surface.Usually the automatic system of the measurement of coordinates machinery of indication is expensive, is again slow, only is used for non-online rather than be used for the continuous on-line quality control.Mechanical gauge, for example mircrometer gauge and calliper, precision is low, and the profile of surface topography can not be provided.So wishing very much has a kind of high speed, the optical measuring device of non-contacting contour of object to be used for non-online and online accurate manufacture process.A kind of like this device should be suitable for various object sizes, surface configuration and texture.This device also should with used self-winding parts adapted in the industrial environment, and be insensitive to vibration.
Prior art provides several optical profile measuring techniques according to geometrical optics.A kind of representative example is More (Moire) fringe analysis.This technology has detailed introduction (Daniel Malacara (Wiley, New York, 1992) in the 16th chapter of " Optical Shop Testing " book.More's method comprises projection and the strange groove of imaging human relations cycle structures such as (ronchi ruling), and with the equivalence of geometric triangulation shape.Based on the commercial product of this principle is the flat mirror of check, by Speedfam-Spitfire production group make (Des plaines, IL).Though the profile on the thick surface of Moire method energy measurement generally is that precision is low than the mechanical system slip gauge, can not be used for the measurement of specular surface in some cases fully.Another difficulty is, the Moire method must be carried out careful calibration to geometric error, and this error bothers when body surface has big degree of depth vibration very much.
Prior art also provides several measuring methods of utilizing optical interdferometer, utilizes the fluctuation property interior change of rendered surface height accurately of light.Several interferometers commonly used can be referring to " Optical Shop Testing " book the 1st chapter, the second edition (content among the Daniel Malacara (Wiley, New York, 1992).Most of habitual existing interference device can not be measured the character of surface that has discontinuous Level Change or surpass the roughness of source light  wavelength.Source optical wavelength 0.63 μ m normally in commercial apparatus.So, can cause the ambiguity of interferometric phase greater than the noncontinuous surface characteristic of 0.16 μ m, this will cause difficulty for further instruction, or impossible.Also have a difficulty to be, when surperficial gradient caused when being difficult to differentiate or distinguish interference fringe greatly.Therefore, do not think that interferometer is applicable to the manufacturing problems of measurement that solution is a large amount of.
Because the limited range of application of conventional interference instrument, prior art provides other interference technique and device, and they can be applicable to thick surface in the surface topography and big variation.A kind of obvious method is to use non-common light source to increase light wavelength.For example by " Rough surface interferometry using a Co 2Leser Source " literary composition (C.R.Munnerlyn, the disclosed content of M.Latta (Appl.opt.7 (9) 1858-1859 (1968)).Yet these methods are normally expensive and trouble, because they comprise special light source, and optics and detector.Also have, these expensive long-wavelength interferometers can not be used under the situation of discontinuous variation above long wavelength's  of surface topography.
Other existing approach that overcomes the limited range of habitual interferometer comprises the use multi-wavelength, as introducing first at " Application desphenomenes d ' interference a des d é terminationsmetrologigues " (J.de Phys.3 (7), 57-68 (1898)) literary composition by R.Ren é Beno ǐ t.A series of measurements of carrying out at two or more wavelength provide considerable effective wavelength, and they can overcome the ambiguity problem of habitual single wave length interferometer.A kind of method that this technology is used for surface measurement is by United States Patent (USP) U.S.No4, and 355,899, " Interferometric distance measurementmethod " (T.A.Nussmier (1982) is open.Yet these multi-wavelength technology become at need to differentiating interference fringe greatly in surperficial gradient or roughness, still can not correctly work.The multi-wavelength interference instrument is also quite responsive to vibration.
Other interferometric methods that provided by prior art are attempted to be different from general measurement geometry by use and are lowered susceptibility to surfaceness and surperficial gradient.A kind of representational desensitization interferometer adopts the pitch angle illumination, for example at United States Patent (USP) U.S.P No.4,325,637 " Phase modulation ofgrazing incidence interferometer " (R.C.Moore), and article " Oblique incidence and observation electronic speckle-pat-tern interferometry " ((Applied Optics 33 (31) for C.Joenathan.B.France.H.J.Tizini, 7307-7311, (1994)) in introduced.In these so-called grazing-incidence interferometers, the illumination at angle of inclination and observation are than interferometer commonly used, with the fringe density that reduces on the body surface.The fringe density of this minimizing is corresponding to an effective wavelength Λ, and it can be than much longer times of the actual wavelength of light.Effective wavelength Λ is big more, can be big more by the degree of instrument reconciliation statement surface roughness.Yet the remarkable reduction of susceptibility needs the big illumination angle with respect to vertical incidence.This big angle will produce many problems to the suitable illumination and the imaging of object.Also may be from character of surface, such as step and striped, undesirable shade produced.Additional complicacy is that the reference light and the thing light of balance interferometer produce with the variation that compensates surface reflectivity owing to needing suitably.Also have, plunder and penetrate interferometer and do not fit into the character of surface that discrete height change surpasses the  of effective wavelength A.
Other with method of geometry that long effective wavelength produces interference pattern is, source light is divided into two bundle light, and they are with the surface of different incidence angles irradiation same section.At these light beam compound tenses, last interference pattern will lower the susceptibility to surperficial morphology change significantly.The fringe density of this attenuating can characterize with an effective wavelength Λ; Yet this method does not need sizable illumination angle, and other benefit is that its intensity of interfering beam is balance.Adopt different angles illumination and observation, can be with the measuring instrument of obtaining a long effective wavelength referring to desensitization interferometer of the present disclosure.
Prior art provides the example of several desensitization interferometers.At article " Opticalcontour mapping of surface " (W.Jaerisch, G.Makosch) (Applied optics 12 (7), 1552-1557 (1973)) once introduced a kind of desensitization interferometer in, its adopt one almost with the contacted diffraction grating of test surfaces.With monochromatic plane wave illumination grating, produce several light beams corresponding to the different diffraction level.These light beams are reflected by body surface, and compound again by grating, form similar in appearance to the stripe of the surface topography of body surface.Other existing method that comprises the light beam of different illumination angles is presented in article " Common-path interferom-eter for flatness testing " (P.Jacquot, X.Colonna deLega, P.M.Boone, SPIE 2248, Optics for productivity inmanufacturing, 18 (1994)) in.This measuring instrument adopts the interaction of two orders of diffraction of the holograph that writes down spherical wave front to come work.
Although people's such as the method for Jaerisch and Makosch and Jacquot method has some advantage, they are not suitable for the automated optical detection, because they do not provide enough operating distances.Two kinds of methods all require as close as possible body surface to place diffraction grating.This is because in two kinds of methods, by a diffraction element source light is divided into the light beam of propagating with different directions, and the same area on illuminated objects surface not.So this two bundles light does not have suitable orientation to produce desirable interference effect, especially on thick surface.The unique method of avoiding this problem is the surface that makes the very close diffraction element of object.Usually, make operating distance, be defined as object to the distance of any parts of interferometer less than 100 μ m.This need be a very little distance to most of production testing.
The desensitization interferometer of two light angles of employing of several forms does not need object almost to contact with the parts of interferometer.A representative example is by United States Patent (USP) U.S.P No.4, and 958,884 (F.H.Smith) are disclosed.The combination that Smith discloses several use refractions and polarization member comes separately and the method for multiple source light, and operating distance is big in this mode.These methods comprise, utilize a Jamin interferometer, a birefringence two-beam device, a birefringence biprism, or a Savart two-beam plate.
Another example of desensitization interferometer with big operating distance is by United States Patent (USP) U.S.P No.4, and 498,771 " Method and means for interfer-ometric surface topography " (G.Makosch (3:37-4:16)) provide.Use a birefringece crystal by the disclosed device of Makosch, for example a Wollaston prism and a level crossing system are incident to object to light beam.
When using broadband or diffuse illumination, the shortcoming of desensitization interferometer is that useful fathoming is subjected to the coherence's of light restriction.Briefly, " coherence " is meant at this, makes light be divided into the ability that two division and combination light time light sources produce interference fringe.Usually, the quality of striped and contrast are along with the two bundle light optical path differences of advancing descend.An incoherent light source is subjected to only producing when optical path difference between accurate localization so that the interfering beam is approximately equal to zero the striped of hard contrast at object.The characteristic of the desensitization interferometer of employing incoherent light source is similar in appearance to white light interferometer commonly used, such as a Miran micro objective, and its difference is that the degree of interference effect is to have strengthened." white light " is meant any illumination herein, and it is to have big spectral distribution and characterize by being compared to laser, can be that low pressure is shown the light source of monochromatic radiation basically such as lamp.Practical result is that light source is incoherent, a striped appearance on the part of the object in the little depth range of interferometer optical axis.This depth range is very little, just several times of effective wavelength.So this is too little for permitting great manufacturing object.
The form of the desensitization interferometer of two angle illuminations of several existing employings is insensitive for the wavelength of light source, so it can be worked with white light the time well.A kind of like this system is open by the U.S. Patent application that awaits the reply " Method andapparatus for profiling surfaces using diffractive optics " (U.S.Serial Nos.08/334 939 and 08/,365 589 is respectively at 1994.11.7 and 1994.12.28 application).Utilize the combination of two or two above diffraction elements, criticize the device described in the patented claim in previous grade, conduct is with reference to content in this article for its content, and it is that measurement face is projeced into a suitable operating distance.Apply for that by these described preferred embodiment has an effective wavelength Λ, it is independent of source wavelength λ basically.So, can use various light sources.Yet if light source is expanded, that is, if it has a big launch site and sends a noncoherent light beam in space thus, striped only appears at and is positioned at along on the position of the object of the little depth range of interferometer optical axis.This depth range also can be very little, just several times of effective wavelength.So this is too little for permitting great manufacturing object.
If body surface is coarse, this is a normal difficulty of meeting for the desensitization interferometer with the different incident beams of all employings angle.Incide lip-deep two the bundle light be positioned at substantially the same local time just might obtain high-quality on a rough surface striped, even source light is be concerned with also like this fully.So, measure only in a little depth range of interferometer optical axis, to carry out when body surface when being coarse.The characteristic that these all geometry are gone up the interferometer of desensitization has seriously limited its serviceability.
Observe as seen from these, existing desensitization interferometer is convenient to have many advantages with the measuring task of a long effective wavelength for some, yet they are being used in the manufacture component measurement that surface topography has big variation many restrictions being arranged.In addition, the desensitization interferometer energy measurement of the above-mentioned introduction of neither one has the noncontinuous surface feature, and perhaps average surface roughness is crossed the object of effective wavelength .
A diverse interfere measurement technique that is used for measuring surface form is based on a mechanical scanning mechanism and the interferometer commonly used with white light work, and in the disclosure, this technology is cited as scanning white light interferometer or SWLI.Utilize an exemplary process of the surface topography three-dimensional measurement of SWLI to be disclosed in United States Patent (USP) U.S.P No.4, among 340,306 (N.Balasubramanian).This patent is introduced a kind of white light interferometer.It comprises a mechanical scanning reference mirror, and a two-dimensional detector displays and computer control.Disclosed method comprises, with the step of separating or to reference mirror scanning, perhaps to object scanning, each pixel of each scanning position measured fringe contrast, and in this way each surface point measured the position of maximum fringe contrast.The scanning position of contrast maximum is the measurement of the relative height of a special list millet cake.Be applicable to measurement as the SWLI method that Bala-Subramanian instructed as some minute surface of used for optical part.
Other existing SWLI technology is because the pending U.S. Patent Application No.08/014 707 " Method and apparatusfor surface topography measurement by spatial-fre quen-cy analysis of interferograms " that submitted on September 9th, 1994 is mentioned.The optical system of the disclosed Measuring Object pattern of this application is the interferometer that has polychrome or white light source by, a mechanical scanner, and a two-way detector array is formed with the digital signal processing device that is used for from interference data mensuration surface elevation.The interferogram of each image point is produced simultaneously by in approximately perpendicular to the surface direction of being thrown light on by interferometer object being scanned in the visual field, and the data of detector are recorded in the digital memory in scanning.Then, utilize these interferograms Fourier to analyze and be transformed into the spatial frequency district, obtain every surface elevation as the complex phase position of spatial frequency function by measuring.Final step is to produce a complete three-dimensional image that is made of altitude information and corresponding image plane coordinate.
Though various existing SWLI method and apparatus are useful to the measurement on certain object and surface, but they all exist some important and basic shortcomings, promptly, little visual field, hypersensitivity to the object reflectance variation, slow Measuring Time for the optical surface of other form is measured, and hypersensitivity to vibrating.These restrictions are relevant with corresponding fringe density with light wavelength.
One of most important shortcoming of existing SWLI method is that the visual field is littler than the visual field of standard microscope eyepiece usually.For Mi mends this, desire to make the detector of the interference data of electrographic recording SWLI instrument to compare and have sufficiently high resolution with interference fringe density.When the visual field of existing SWLI instrument increases, fringe density be easy to become Tai Gao so that can not differentiate, especially particularly like this when handling rough surface.Gradient tolerance limit for the mirror surface is to reduce with the visual field size linearly, if several apertures (NA) of object lens increase with the visual field and descend linearly simultaneously, is soluble to the needed speckle effect of thick surface measurement then.For the needs that solve thick surface marking effect is least to encourage the thing done, because the amount of gathered light is along with square decline of NA.Light loss is meant that bigger surface needs a stronger luminaire.What is worse, fringe contrast is a very variable parameter now, and the quality of measuring depends primarily on the balance between reference beam and the object beam intensity.
Owing to measure the difficulty of big surface area, according to the unique commercial measuring instrument that gets of SWLI is microscope, usually it has the round visual field of a diameter less than 5mm, New viewl00 type (Zygo company) for example, RST (WYKO company (Tucson, AZ), MICROXAM-EX (Phase-shift Tech-nologie (Tucson, AZ) and 512 optical profilometers (MicroMap (Tuc-son, AZ).So no matter the survey instrument basic demand that is used to make how, prior art does not provide the SWLI instrument to have anything that is different from microscope components.
Other major defect of existing SWLI technology is, data acquisition is very slow, and by the RST that WYKO company makes, for example its data acquisition rate is per second 0.5 a μ case depth.Surface with 1mm surface characteristics need be with scanning more than 30 minutes.Slow speed is the result as the vertiginous interference effect of scanning position function.Accurate measurement requirement changes detail record to these, and common every scanning motion 75nm carries out one-shot measurement to every pixel.Jogging speed also can produce other subsidiary problem, as when measuring to the high sensitive of vibration, problems such as thermal deformation and mechanical strain.
Other major defect of SWLI is, to the high sensitive of vibration, this part is because slow acquisition speed, and part is because due to the quite high susceptibility of interference fringe pattern, and this vibration is easy to be caused by very in a small amount vibration.The SWLI measuring instrument generally requires integral installation and expensive vibration isolation.Although adopt these preventive measure, the SWLI instrument still is limited to be used in the environment of comparing relatively placidity with normal production environment.
Because to high speed, pressing for of large tracts of land instrumentation manufacture component has the multiple range of application of attempting to expand SWLI.For example, by article " Three-di-mensional imaging by sub-Nyquist Sampling of white-light interferograms " (P.de Grout, L.Deck (opt.Lett.18 (17), 1462-1464 (1993)) described method, it comprises, the sparse data sampling so that improve acquisition speed, thereby improves the depth range of measuring instrument.Yet even adopt the sparse data sampling, the SWLI method is still slow, because need be to the cause of the accurate sampling of high density interference fringe pattern.Other prior art is to increasing the effort of measuring speed at United States Patent (USP) U.S.P No.5 in a SWLI microscope, 402, open in 234 (the 1995.3.28 announcements) by name " Method andApparatus for the Rapid Acquisition of Data in CoherenceScanning interferometry " (L.Deck), utilize a kind of special algorithm and data buffer to select and the useful part of storing interferogram is used for each pixel by the described system of Deck.This method reduces data processing amount that three-dimensional image is required of generation in fact.Principle by the Deck instruction has been used on the New View-100 type product (by Zygo company manufacturing (Middle-field, CT)).Yet New View 100 still needs the precise information sampling of high density interference fringe pattern.Thus, measuring speed is still very slow, is still the speed sampling with per second 2 μ case depths.
Other increases attempting by T.Dresel of the useful application of SWLI, G.Haeusler, introduce in the article that H.Venzke delivered " Three-dimensionalsensing of rough surfaces by coherence rader " (Applied op-tics 31 (7), 919-925 (1992)).Disclosed optical system has an adjustable NA.Can be from big, rough surface increases the average speckle size and makes two combinations that mechanical actuator is special, and actuator makes reference mirror at an intrinsic displacement among a small circle, and another scans object with discontinuous step.Several accompanying drawings in the literary composition are represented the image of three-dimensional body, and the diameter of this object is greater than 5mm.Yet low light value is used for big object, and the requirement of handling mass data has seriously limited the practical value of measuring instrument.Equally, data acquisition step is slow especially, is not suitable for optical detection fast.
So, existing increase SWLI serviceability attempt be summarized as follows: mechanical contact pilotage is used to measure some character of surface, but very slow, finite information only is provided, and may damages body surface; Existing optics instrument based on geometrical optics its precision usually and is not all can work to all types of surfaces less than the measuring instrument of mechanical contact pilotage; Interferometer commonly used is the very high-precision measurement that is used for optical element, but is not suitable for a large amount of production testing tasks; The multi-wavelength interference instrument can solve by step on the minute surface and caused some the ambiguity problem of texture, but is subjected to as the surperficial gradient of single wave length interferometer and the same restrictions of roughness; The desensitization interferometer is used in the big effective wavelength of one of the easiest usefulness, and to see the surface of looking be advantageous, if but the surface has a big degree of depth vibration than effective wavelength, perhaps when its discontinuous feature of surface greater than 1/4th of effective wavelength, then this interferometer can not fine work; The SWLI method has little visual field, is responsive to the change of surface reflection, and is very slow, quite responsive to vibration.
So although the accurate non-contact optical device that contour of object is measured of making has urgent demand, prior art still can not provide such device.The method of known optical surface measuring wheel exterior feature is not suitable for industrial environment, the size on the surface, and form and texture aspect do not have enough dirigibilities yet, and are not suitable for operating with automatic parts.Discontented thus being enough to accurately, at a high speed and flexibly method and apparatus is used for the requirement of precision measurement surface topography.
By a desensitization interferometer with light illumination, used light source for example can be an incandescent lamp according to optical profile measuring instrument provided by the present invention, a light emitting diode or a laser instrument.The desensitization interferometer is characterized in that having an effective wavelength Λ greater than source wavelength λ; One to the suitable operating distance of object (for example, greater than 1mm), and the ability that produces the hard contrast interference fringe in the depth range L that is limited by equivalent coherent length.Camera with photodetector array is changed interference pattern to interference fringe, becomes the electric signal of whole cell array.
In the visual field of interferometer, for one or more image points, promptly the measurement data of pixel is by making object produce with respect to the interferometer displacement is a certain amount of, and simultaneously the photodetection data is recorded in the electronic memory.Can describe with the approximate oscillator signal relevant with effective wavelength Λ as the function of scanning position for Strength Changes, this signal is subjected to interference effect is limited in a signal envelope of equivalent coherent length L scope and modulates.Oscillator signal is corresponding to interference fringe, and the envelope of oscillator signal is the contrast of striped.
So, come the analysis to measure data by computing machine, measure surface elevation corresponding to each image pixel.For example, in the methods of the invention, be the measurement of the relative height of a special list millet cake for maximum scanning position for fringe contrast.And, in other method of the present invention, interferogram is transformed into the spatial frequency zone with the Fourier analysis, utilize to measure and obtain every surface elevation as spatial frequency function composite phase.
The present invention overcomes the measurement range restriction of existing desensitization interferometer, provides one simultaneously than bigger visual field of all existing scanning white light interferometers and the sweep velocity of Geng Gao.
Of the present invention many will levy by the following description and detailed description with the accompanying drawing spy more clear.
Fig. 1 represents the critical piece synoptic diagram of the inventive method and system.
Fig. 2 represents the curve map of measured intensity as the function of the scanning position of in the visual field pixel.
Fig. 3 represents that one of the present invention is selected for use the embodiment diagrammatic sketch.
Fig. 4 represents the present invention, and another selects the embodiment diagrammatic sketch for use.
Fig. 5 represents the present invention, and another selects the embodiment diagrammatic sketch for use.
Fig. 1 represents a preferred embodiment of optical profile measuring system of the present invention, is used for the surface profile of Measuring Object 20.Provide illumination by light source 30, used light source can be, incandescent lamp for example, a light emitting diode or a plurality of diode, a lighting source that has the spatial independences such as laser instrument of diffuse component.Light beam 40 directive interferometers 50 are preferably selected a desensitization interferometer for use.Interferometer 50 usefulness light beams 60 illuminated objects, described light beam 60 can be made up of two bundles or multi beam (not shown) light, and they are in the substantially the same position of object but with the different incidence angles illuminated objects.Interferometer 50 preferably has following characteristic: effective wavelength Λ is greater than source wavelength λ; Proper operation distance to object 20 is for example greater than 1mm; And ability with generation hard contrast interference fringe in by equivalent coherent length restricted portion L.Interferometer 50 preferably is projected on the electron detector 80 via the interference pattern of light beam 70 with a representative surface, and described electron detector can be, closed-circuit TV camera for example, a kind of linear detector array, or a unit piece detector.
Object 20 preferably is installed on the mechanical scanning worktable 90, can make object 20 at the surface direction top offset that is substantially perpendicular to by the interferometer illumination.Make the displacement of object 20 be referenced herein as depth scan by worktable 90.Worktable 90 preferably is subjected to the control of computing machine 100, in a method for optimizing of the present invention, when object 20 is made continuous depth scan, carries out the measurement of many intensity by electron detector 80.The result of these measurements preferably is stored in the dynamic storage (not shown) of computing machine 100.The data of being gathered are stored as the array of interferogram with digital format thus, in the visual field of interferometer, one of each image point or pixel are all represented the variation of intensity as the scanning position function.
A typical measured intensity is seen shown in Figure 2 as the variation of single pixel depth function.Periodic swinging is cited as interference fringe usually, preferably is limited in the depth range that provides by following formula,
|p+Z-Z o|≤L/2 (1)
Wherein, L is equivalent coherent length, and p is the local surfaces height, and Z is a scanning position, Z oIt is constant.Usually the p value changes along with the difference of the position on the body surface, and it is a kind of measurement of object surface appearance.By object is scanned on a large scale at one, just can collect the interferogram of all surface point.
The method of several analysis interferograms as shown in Figure 2 is known in the past.Straightforward procedure comprises, measures the oscillator signal intensity as the analyzing spot function of position in interferogram.At p=Z oSignal is the strongest during-Z.So signal intensity is an indication to the surface elevation p of each pixel.The very large variation of the possible Measuring Object surface topography of this method, even these change not in the scope of effective coherent length L.In addition, this analysis can be undertaken by frequency-domain analysis, promptly according to U.S. patented claim " the Method and Apparatus for surface To-pography Measurement by Spatial-Freqnency; Analysisof interferograms " (the U.S. application number No.08/014 that instructs that awaits the reply, 707,1994.9.9 submit to), described content is as the reference of originally quoting.
So data acquisition of the present invention and the side of analysising are similar to and have that the SMLI system adopted.Yet, because the interferogram of apparatus of the present invention is characterized in that effective wavelength Λ is different from source wavelength λ, thus to the required number of data points of given sweep length than the prior art factor lambda/Λ that will descend.In addition, the electron detection device can be than the easier resolution coherent fringe of interference pattern that characterizes with the optics wavelength X.So than prior art, survey area substantially can obtain increasing.
Though in its operation of various embodiment disclosed herein is with an incoherent light source, also may obtain purpose of the present invention with spatially coherent light, just can to the catoptrical spatial coherence that is enough to fall progressively basically as long as body surface is coarse.Basic demand is that interferometer is characterized in that equivalent coherent length L is not undue length.Data analysing method as far as is known, the general range of useful equivalent coherent length is provided by following formula:
3Λ≤L≤30Λ (2)
Though other L value also may not depart from spirit of the present invention.
Referring to Fig. 3, it represents one embodiment of the present of invention, add the desensitization interferometer of a special shape among the described embodiment that selects for use, it is according to the pending U.S. Patent Application of our unity of possession " Method and Apparatns ofr pro-filing surface using Diffractive optics " (U.S. series number No.08/334 939,1994,11,7 submit to, and U.S. series number No.08/365589, and 1994,12,28 submissions) instruction.Adopt the method for this device according to the present invention, the light of light source 30 becomes illuminating bundle 140 by lens 35 collimations, and light beam 140 at first is incident to grating 120, by grating 120 light beam 140 is divided into light beam 150 and light beam 160.Next step, light beam 150 and 160 is penetrated on object 20 basically by second diffraction grating, 130 diffraction.By reflecting on the object, light beam is towards grating 130 back-propagatings, by grating 13 by this way with beam diffraction, even they close light on the surface of grating 120, be diffracted into a branch of common outgoing beam 180 through compound light then, and this light beam is gathered on the camera 50, by the interference pattern of camera detection corresponding to light beam 150 and 160 optical path differences.
Because the different incidence angles of light beam 150 and 160, the perpendicular displacement of object 20 will cause the variation of measured intensity as depth function.
This pixel that is used for measuring image is identical with shown in Fig. 2 basically as the Strength Changes of scanning position function, so can adopt effective wavelength Λ and equivalent coherent length L to characterize.Effective wavelength can calculate from following formula: Λ = λ Cos ( θ ) - Cos ( φ ) - - - - - - ( 3 ) Wherein, θ is the incident angle of light beam 160 with respect to the surface 170 of object 20, and φ is the incident angle of light beam with respect to the surface 170 of object 20.As seen, any in principle effective wavelength Λ 〉=λ all can produce by suitable selected angle φ.For example, if, φ=20 °, θ=0 °, then Λ ≈ 16.6 λ.
Equivalent coherent length L embodiment illustrated in fig. 3 is depended on many factors, but mainly relevant with the size of the light launch site of the surfaceness of object 20 and light source 30.So if the size of light launch site is adjustable, if perhaps the spatial coherence of light source is variable, the size that then can regulate equivalent coherent length L is to being suitable for application.
Referring to Fig. 4, expression the present invention adopts the embodiment of the desensitization interferometer of another kind of form.In the embodiment shown in fig. 4, the light that light source 230 sends is collimated into light beam 200 with lens 235, light beam 200 is by enocscope 205 reflections, beam splitter 210 is divided into light beam 240 and light beam 245 to light, light beam 240 is by mirror 250 reflections, and being incident to object 20 with incident angle φ, light beam 245 is by mirror 255 reflections, and is incident upon object 20 with incident angle θ.Light beam is after object 20 reflection, and light beam 245 and light beam 255 from mirror 260 and 265 reflections, combine light into light beam 275 by beam splitter 270 respectively then, lens 285 with object 20 imaging on camera 290.When suitably regulating, embodiment illustrated in fig. 4 in the stroke of different light beams will cause an interference pattern, but this is under the simplification effective wavelength Λ situation given by equation (3).When suitably regulating, interferometer will be as the function of an incoherent light source.Yet when using an incoherent light source in present embodiment, high fringe contrast zone is restricted in the equivalent coherent length L.The spectrum width and the size of equivalence coherent length and light source all have relation.Further feature embodiment illustrated in fig. 4, for example, data acquisition and analytical procedure, substantially the same in the previously described embodiment of the present invention.
Referring to Fig. 5, it represents that the present invention adopts the another embodiment of the desensitization interferometer of another form.In the embodiment shown in fig. 5, the light that light source 330 sends becomes light beam 300 by lens 335 collimations, light beam 300 is divided into the light beam 340 and 345 of two bundle mutually orthogonal polarizations by portion of birefringence unit, and used birefringence element can be that a Wollaston prism etc. is used for the light beam space is divided into two optical elements of restrainting polarized lights.Lens 350 focus on light beam 340 and 345 on the object 20 together.After object 20 reflections, light beam 340 and 345 is dispersed up to them burnt by lens 360 remittances, and lens 360 focus on the back to light beam once more together.Birefringence element 370 combines light into light beam 375 with light beam 340 and 345.Polarizer 380 is orientated, and makes the projection of light beam 340 and 345 synthesize a polarization altogether, causes a kind of interference effect.Afterwards, lens 385 make image formation of object to camera 390.When suitably regulating, the different light paths in embodiment illustrated in fig. 5 will form the interference pattern of representing object appearance, but this is under the situation of the simplification effective wavelength Λ given by equation (3).Under suitable adjusting situation, interferometer also will be as the function of incoherent light source.Yet when present embodiment used an incoherent light source, high fringe contrast zone was restricted in the equivalent coherent length L.The spectrum width and the size of equivalence coherent length and light source all have relation.Single-point or the linear image that is suitable for most object 20 embodiment illustrated in fig. 5.Under the situation of single-point or linear image, can prove that it is useful adding in the worktable to transversal scanning mechanism (not shown), thereby can simplify the formation of the three-dimensional profile profile of a complete object 20.Further feature embodiment illustrated in fig. 5, such as data acquisition and analytical procedure are substantially the same in the previously described embodiment of the invention.
The person skilled in the art will understand, additional replacement, omission and change in form, or the details of the device of disclosed method can be made in the case of without departing from the spirit of the present invention.
In a word, the present invention interfere profile measurer and method and some advantage conclude as Lower: as to measure thick surface and mirror surface; The energy measurement has large deformation and big gradient The surface: potential visual field is greater than existing SWLI technology; Compare existing SWLI Technology has higher measuring speed; Comparing existing desensitization interferometer has big dark The degree scope; Compare most of existing desensitization interferometer and have bigger operating distance; Reduce than the susceptibility of the existing interferometer of major part to vibration; Because two bundle phases The fabulous fringe contrast that dried light beam brings from the body surface reflection.

Claims (33)

1. a method of utilizing the desensitization interference fringe of desensitization interference device to body surface measurement profile comprises the steps:
Utilization has the described desensitization interference device of light illumination of relevant wavelength, and described desensitization interference fringe is provided, and described its effective wavelength that is had of desensitization interference device is greater than the relevant wavelength of described light source and have a relevant equivalent coherent length;
In the visual field of described desensitization interference device, produce the measurement data of at least one image pixel, this generation data are to realize by making described object provide an intensity that changes with scanning position to change with respect to the displacement of desensitization interference device, described intensity changes signal relevant with described effective wavelength of formation, and this intensity change is subjected to a modulation that makes any interference effect be limited in the equivalent coherent signal envelope in the equivalent coherent length scope; Described signal is corresponding to described interference fringe, and the relevant envelope of described equivalence is corresponding to the fringe contrast of described striped;
Analyze described measurement data, be equivalent to the surface elevation of each described image pixel with mensuration.
2. according to the method for claim 1, it is characterized in that measurement data produces step and comprises, the array of whole image pixel is changed the step of described interference pattern.
3. according to the method for claim 2, it is characterized in that described switch process comprises the step of utilizing the camera that comprises the light prober array to change described interference pattern.
4. according to the method for claim 2, it is characterized in that described analytical procedure comprises, utilizes the step of the described measurement data of Computer Analysis.
5. according to the method for claim 1, it is characterized in that described analytical procedure comprises, utilizes the step of the described measurement data of Computer Analysis.
6. according to the method for claim 1, it is characterized in that described measurement data produces step and comprises, it is maximum known scanning position that a described fringe contrast is provided, the step of measuring with the relative height that is provided at a mark sheet millet cake on the described body surface.
7. according to the method for claim 1, it is characterized in that, described measurement data produces step and also comprises, described interference pattern is transformed into the step in spatial frequency zone, described analytical procedure comprises, check whether described transform interference pattern is the function of spatial frequency, to be provided at the step of the surface elevation of each point on the described body surface.
8. according to the method for claim 7, it is characterized in that described shift step comprises, utilizes the described interference pattern of Fourier analysis conversion to become the step in spatial frequency zone.
9. according to the method for claim 1, it is characterized in that described illumination step comprises, with the step of a described desensitization interference device of LASER Light Source illumination.
10. according to the method for claim 1, it is characterized in that described illumination step comprises, with the step of a described desensitization interference device of incandescent light source illumination.
11. the method according to claim 1 is characterized in that, described illumination step comprises, with the step of a light emitting diode light source light according to described desensitization interference device.
12. the method according to claim 1 is characterized in that, described illumination step also comprises, the step of the desensitization interference fringe of hard contrast is provided in the depth range of described equivalent coherent length.
13. the method according to claim 1 is characterized in that, described measurement data produces step and comprises that the described object of depth scan is to provide the step of described Strength Changes as the function of described scanning position.
14. the method according to claim 13 is characterized in that, described depth scan step comprises, makes object in the step that is substantially perpendicular to by the surface direction displacement of described desensitization interference device illumination.
15. the method according to claim 14 is characterized in that, described measurement data produces step and also comprises, realizes repeatedly the step of ionization meter when depth scan object continuously, and the array of interference is provided, and the first is to every point measurement of described image pixel.
16. the method according to claim 13 is characterized in that, described measurement data produces step and also comprises, realizes repeatedly the step of ionization meter when depth scan object continuously, and the array of interferogram is provided, and the first is to every point measurement of described image pixel.
17. the method according to claim 1 is characterized in that, described scope with equivalent coherent length comprises, by formula:
| p+Z-Z o| the depth range of≤L/2, wherein L is described equivalent coherent length, and p is the local surfaces height on described body surface, and Z is a scanning position, Z oBe a constant, p changes along with the position on the described body surface thus, also comprises the pattern on Measuring Object surface.
18. the method according to claim 1 is characterized in that, described measurement data produces step and comprises, makes the step of described object with respect to a known quantity of described desensitization interference device displacement, and almost at the same time the photodetection data is recorded in the electronic memory.
19. the method according to claim 18 is characterized in that, described measurement data produces step and also comprises, the array of whole image pixel is changed described interference pattern, so that described photo-detector data to be provided.
20. the method according to claim 1 is characterized in that, described proper operation distance is greater than the degree of depth of structure on the described body surface.
21. the method according to claim 1 is characterized in that, described signal comprises an approximate oscillator signal.
22. the method according to claim 18 is characterized in that, described signal comprises an approximate oscillator signal.
23. the wide system of optics measuring wheel that is used for the surface profile of Measuring Object, described system comprises, lighting device, described lighting device have a relevant wavelength; The desensitization interference device, be arranged to be subjected to it to shine with respect to lighting device, but described interference device carries out illumination in substantially the same place to described object with multiple beam different incident angles, its relevant effective wavelength of described interference device is greater than the relevant wavelength of described lighting device and have a relevant equivalent coherent length, and described interference device can produce the interference fringe of hard contrast in the equivalent coherent length restricted portion by described interference device; Sniffer is arranged to detectable interference fringe with respect to described interference device; Scanister is placed in the top of described object and is arranged to make described object with respect to the surface displacement by described interference device illumination, the depth scan of described object is produced an intensity that changes with scanning position changes to provide; Described intensity changes signal relevant with described effective wavelength of formation, described intensity change is subjected to a modulation that makes any interference effect be limited to the equivalent coherent signal envelope in the described scope, described signal is corresponding to described interference fringe, the relevant envelope of described equivalence is corresponding to the fringe contrast of described striped, described detection Strength Changes is to provide the interferogram of at least one image pixel in the visual field of described profile measurer; And device that is used to be provided on the described surface at least corresponding to the surface elevation of a described image pixel.
24. according to the wide system of the optics measuring wheel of claim 23, it is characterized in that described sniffer comprises, each image pixel is provided the device of interferogram in described visual field, described surface elevation generator comprises, each described image pixel is provided the device of surface elevation.
25. according to the wide system of the optics measuring wheel of claim 23, it is characterized in that, described scanister comprises, is used to provide the device that described object is carried out continuous depth scan, and described sniffer carries out corresponding many ionization meters to the continuous depth scan of object the time.
26., it is characterized in that described dark survey device comprises that also storing apparatus is used to store described detection interferogram according to the wide system of the optics measuring wheel of claim 25; Described surface elevation generator is used for providing described surface elevation from the interferogram of storage.
27., it is characterized in that described scope is by tabular form according to the wide system of the optics measuring wheel of claim 23 | p+Z-Z o|≤L/2 provides, and wherein L is the relevant wavelength of equivalence, is the situation surface elevation, and Z is a scanning position, Z oBe constant, p changes with the surface of position on the described body surface, and comprises the measurement to object surface appearance.
28., it is characterized in that described lighting device comprises a space incoherent illumination light source according to the wide system of the optics measuring wheel of claim 23.
29., it is characterized in that described lighting device comprises a laser instrument according to the wide system of the optics measuring wheel of claim 23.
30., it is characterized in that described lighting device comprises an incandescent lamp according to the wide system of the optics measuring wheel of claim 23.
31., it is characterized in that described lighting device comprises the light emitting diode device according to the wide system of the optics measuring wheel of claim 23.
32., it is characterized in that described signal comprises an approximate oscillator signal according to the wide system of the optics measuring wheel of claim 23.
33. according to the wide system of the optics measuring wheel of claim 23, it is characterized in that, described sniffer comprises light detection device, described scanister comprises, make described object with respect to the certain amount of described interference device displacement, and survey the device of described Strength Changes in displacement simultaneously with described light detection device.
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